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.\" $Id: form_fieldtype.3x,v 1.20 2020/02/02 23:34:34 tom Exp $
.TH form_fieldtype 3X ""
.SH NAME
\fBform_fieldtype\fR \- define validation-field types
.SH SYNOPSIS
\fB#include <form.h>\fR
.br
FIELDTYPE *new_fieldtype(
    bool (* const field_check)(FIELD *, const void *),
    bool (* const char_check)(int, const void *));
.br
int free_fieldtype(FIELDTYPE *fieldtype);
.br
int set_fieldtype_arg(
    FIELDTYPE *fieldtype,
    void *(* const make_arg)(va_list *),
    void *(* const copy_arg)(const void *),
    void  (* const free_arg)(void *));
.br
int set_fieldtype_choice(
    FIELDTYPE *fieldtype,
    bool (* const next_choice)(FIELD *, const void *),
    bool (* const prev_choice)(FIELD *, const void *));
.br
FIELDTYPE *link_fieldtype(FIELDTYPE *type1,
                          FIELDTYPE *type2);
.br
.SH DESCRIPTION
The function \fBnew_fieldtype\fR creates a new field type usable for data
validation.
You supply it with \fIfield_check\fR, a predicate to check the
validity of an entered data string whenever the user attempts to leave a field.
The (FIELD *) argument is passed in so the validation predicate can see the
field's buffer, sizes and other attributes; the second argument is an
argument-block structure, about which more below.
.PP
You also supply \fBnew_fieldtype\fR with \fIchar_check\fR,
a function to validate input characters as they are entered; it will be passed
the character to be checked and a pointer to an argument-block structure.
.PP
The function \fBfree_fieldtype\fR frees the space allocated for a given
validation type.
.PP
The function \fBset_fieldtype_arg\fR associates
three storage-management functions with a field type.
The \fImake_arg\fR function is automatically applied to the
list of arguments you give \fBset_field_type\fR when attaching validation
to a field; its job is to bundle these into an allocated argument-block
object which can later be passed to validation predicated.
The other two hook arguments should copy and free argument-block structures.
They will be used by the forms-driver code.
You must supply the \fImake_arg\fR function,
the other two are optional, you may supply NULL for them.
In this case it is assumed
that \fImake_arg\fR does not allocate memory but simply loads the
argument into a single scalar value.
.PP
The function \fBlink_fieldtype\fR creates
a new field type from the two given types.
They are connected by an logical 'OR'.
.PP
The form driver requests \fBREQ_NEXT_CHOICE\fR and \fBREQ_PREV_CHOICE\fR assume
that the possible values of a field form an ordered set, and provide the forms
user with a way to move through the set.
The \fBset_fieldtype_choice\fR
function allows forms programmers to define successor and predecessor functions
for the field type.
These functions take the field pointer and an
argument-block structure as arguments.
.SH RETURN VALUE
The pointer-valued routines return NULL on error.
They set errno according to their success:
.TP 5
.B E_OK
The routine succeeded.
.TP 5
.B E_BAD_ARGUMENT
Routine detected an incorrect or out-of-range argument.
.TP 5
.B E_SYSTEM_ERROR
System error occurred, e.g., malloc failure.
.PP
The integer-valued routines return one of the following codes on
error:
.TP 5
.B E_OK
The routine succeeded.
.TP 5
.B E_BAD_ARGUMENT
Routine detected an incorrect or out-of-range argument.
.TP 5
.B E_CONNECTED
The field is already connected to a form.
.TP 5
.B E_CURRENT
The field is the current field.
.TP 5
.B E_SYSTEM_ERROR
System error occurred (see \fBerrno\fR(3)).
.SH SEE ALSO
\fBcurses\fR(3X), \fBform\fR(3X).
.SH NOTES
The header file \fB<form.h>\fR automatically includes the header file
\fB<curses.h>\fR.
.PP
All of the \fB(char *)\fR arguments of these functions should actually be
\fB(void *)\fR.  The type has been left uncorrected for strict compatibility
with System V.
.SH PORTABILITY
These routines emulate the System V forms library.
They were not supported on
Version 7 or BSD versions.
.SH AUTHORS
Juergen Pfeifer.
Manual pages and adaptation for new curses by Eric S. Raymond.
